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13-01-89/T\PEN00
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » CEEFAX disks » telesoftware12.adl |
| Filename: | 13-01-89/T\PEN00 |
| Read OK: | ✔ |
| File size: | 2C6A bytes |
| Load address: | 000D |
| Exec address: | 0000 |
File contents
Using a light pen with the BBC microcomputer - by - Gordon Horsington
---------------------------------------------------------------------
Module 0. Introduction
----------------------
Light pens can be used with the BBC B, BBC B+ and Master 128 computers.
This module introduces a block of six modules which deal with the design
of both the hardware and software needed to use a light pen with a BBC
microcomputer.
The six modules are in files named T/PEN00 to T/PEN05. The following
topics will be covered in these modules.
Module 0. This module. Designing and testing a light pen.
Programs: PENTEST, RHBOOT
Module 1. Introduction to light pen software.
Program: OFFSET
Module 2. Light pen interrupts.
Program: IOINTER
Module 3. Tube compatible, interrupt driven, scrolling light pen software.
Program: SPINTER
Module 4. Using a light pen for graphics input.
Program: GRAPHIC
Module 5. Sideways RAM light pen drivers.
Programs: SWTEXT, SWGRAPH, ARTIST
The later modules develop the ideas and techniques described in the
earlier modules and for this reason they need to be worked through from
beginning to end rather than used as a reference guide. It is essential to
have either BASIC 2 or BASIC 4 and operating system 1.20 (or higher)
installed in your computer.
Light pen design
----------------
A light pen generates a TTL pulse called a video strobe pulse (VSP) and
the timing of this pulse corresponds with the position of the pen on the
screen. The screen position at the falling edge of the VSP is latched into
the 14 bit light pen register of the 6845 CRTC in the computer. The Acorn
approved light pen uses a push tip micro switch to signal to the computer
when the tip of the pen is touching the video monitor screen. The switch
is connected the right fire button input (PB1 of the analogue port
connector) and is normally closed. This means that when the pen is
touching the screen then ADVAL(0)AND3=0, and when the pen is not pressed
against the screen ADVAL(0)AND3=2. Using a normally closed switch is quite
a good idea because software written for the Acorn approved design light
pen can be used with a pen which does not have a switch without modifying
the software. If you decide to make your own light pen try to incorporate
a normally closed switch across pin 3 (0 Volts) and pin 10 (PB1, also
known as IO1) of the analogue port connector.
Only one design of light pen has been officially approved by Acorn for use
with the BBC micro. This is the RH Electronics Colour Light Pen. If you
choose to construct your own pen it is not necessary to copy the quite
complicated RH design but, if you use the very simple design described in
this module, you can make a pen that is compatible with software written
for the Acorn approved instrument. The techniques and software described
in the light pen modules can be used without modification on any RH
compatible light pen but they can be adapted for use with almost any other
type of BBC light pen.
The light sensitive device used to construct a light pen should be a
Honeywell sweet spot Schmitt reciever, or a compatible device. These can
be bought from RS Components stockists, part number 303-292. The sweet
spot has a built in lens and amplifier and it is suitable for direct
connection to the BBC micro. Do not use a pin photo diode which will need
an external amplifier if it is to be connected to a BBC computer. The
connections to the analogue port for both the sweet spot and the normally
closed switch are shown in figure 1. Pin 1 of the sweet spot is nearest
the tag and pin 3 is furthest away. The 15 pin D connector required for
the analogue port can also be obtained from RS Components stockists.
Maplin also supply a new, easy to connect, 15 pin D conector.
normally
closed switch
+---------------------------+ +------- pin 3 of sweet spot (0 Volts)
| | |
| 8 7 6 5 4 3 2 1 -- pin 1 of sweet spot (+5 Volts)
\
| 15 14 13 12 11 10 9 ---- pin 2 of sweet spot (output)
| |
+----------------------------+
Figure 1. View into the analogue port showing light pen connections
-------------------------------------------------------------------
The body of the pen can be any suitable tube which allows the light sensor
to be glued into one end. Constructing a press switch operated by touching
the screen would be quite tricky and probably the best substitute is to
attach a finger operated switch to the side of the pen barrel. It is not
essential to have a light pen switch, the space bar or any other keyboard
switch can be just as effective. It is a good idea to construct a light
shade from an opaque pen cap with a hole cut into its sharp end. This can
be placed over the photo sensor when the pen is being used and will
improve the resolution of the light pen quite dramaticly.
It will cost about `14 to construct a light pen. You can buy ready made
BBC light pens for about `20 and you might think that it is hardly worth
the trouble of making one yourself. If you do not have any experience of
soldering components or feel unsure about the connections to be made then
do not attempt to make a light pen yourself. If you buy a pen then try to
get one with a normally closed switch on PB1 (IO1).
If you buy the rather expensive RH Electronics light pen then you will
need to use the program RHBOOT to generate a !BOOT file which must be used
to initialise the pen before using any of the software described in this
series. Cassette users with an RH light pen should *RUN $.!BOOT before
using the pen. Disc users with an RH light pen just need to press
Shift+Break as normal with $.!BOOT files. The program RHBOOT is not needed
with any other light pen.
10 REM> RHBOOT
20 REM use to create an RH light pen !BOOT file
30 DIM mcode &100
40 firstbyte=&2F00
50 drb=&FE40
60 ddrb=&FE42
70 pcr=&FE4C
80 ifr=&FE4D
90 ier=&FE4E
100 oswrch=&FFEE
110 FOR pass=4 TO 6 STEP 2
120 O%=mcode
130 P%=firstbyte
140 [ OPT pass
150 EQUW &FF0D
160 .start
170 LDA drb
180 AND #&20 \ %00100000
190 BEQ return
200 SEI
210 LDA #&08 \ %00001000
220 STA ifr
230 STA ier
240 LDA pcr
250 AND #&7F \ %01111111
260 ORA #&60 \ %01100000
270 STA pcr
280 LDA ddrb
290 AND #&CF \ %11001111
300 STA ddrb
310 LDA ddrb
320 ORA #&30 \ %00110000
330 STA ddrb
340 LDX #&06
350 .delay1
360 DEX
370 BNE delay1
380 LDA ddrb
390 AND #&EF \ %11101111
400 STA ddrb
410 LDX #&64
420 .delay2
430 DEX
440 BNE delay2
450 LDY #&08
460 LDA #&93 \ %10010011
470 .mainloop
480 ASL A
490 PHA
500 LDA ddrb
510 BCS carryset
520 ORA #&20 \ %00100000
530 BNE notzero
540 .carryset
550 AND #&DF \ %11011111
560 .notzero
570 STA ddrb
580 LDA ddrb
590 ORA #&10 \ %00010000
600 STA ddrb
610 AND #&EF \ %11101111
620 STA ddrb
630 LDX #&32
640 .delay3
650 DEX
660 BNE delay3
670 PLA
680 DEY
690 BNE mainloop
700 CLI
710 LDA drb
720 AND #&20 \ %00100000
730 BNE return
740 LDX #&00
750 .print
760 LDA message,X
770 BEQ return
780 JSR oswrch
790 INX
800 BNE print
810 .return
820 RTS
830 .message
840 EQUS "Press <BREAK> to initialise light pen"
850 EQUD &000A0A0D
860 .lastbyte
870 ]
880 NEXT
890 *OPT1,2
900 OSCLI("SAVE $.!BOOT "+STR$~(mcode)+"+"+STR$~(lastbyte-firstbyte)
+" "+STR$~(&FFFF0000 OR start)+" "+STR$~(&FFFF0000 OR firstbyte))
910 *OPT0,0
920 *OPT4,2
In theory, it should be possible to connect a light pen to a Master
Compact computer using the joystick port. The light pen strobe and the
User Port CB2 handshake line appear to share the same pin on the joystick
connector. The User Port data lines PB0 to PB4 and CB1 are also available
on the joystick connector so that a light pen switch could be connected. I
have not used a light pen with a Compact computer and, if a light pen does
work on this machine, the software described in this series will have to
be modified to operate on the User Port rather than the system VIA.
Testing your light pen
----------------------
If you have built your own light pen you will need to test it before going
on to consider the design of light pen driver software. The light pen will
produce a positive going TTL pulse whenever the sensor picks up light
given out by the monitor screen. When the light pen strobe falls back from
logic 1 to logic 0 a number which corresponds with the light pen position
will be stored in registers 16 and 17 of the 6845 CRTC. Light pens are not
sensitive to black because light is not given out by the screen where
black is displayed. Some photo sensors are not sensitive to the red light
given out by some monitor screens. This is because red is at the low
energy end of the visible spectrum of light and can be below the energy
threshold of the photo sensor. To test the light pen it is best to flood
the screen with blue light and examine the contents of registers 16 and 17
of the CRTC as the pen is moved around the screen.
The 6845 CRTC is mapped onto sheila addresses &FE00 and FE01. The 14 bit
light pen register is in register 16 (high byte) and register 17 (low
byte) of the 6845. In order to gain access to any of the 6845 CRTC
registers, the register address must first be written into &FE00, the
address register. After writing a 5 bit address into the address register,
the selected CRTC register may be written to or read from &FE01, the data
register. For example, to read the contents of CRTC register 17 you have
to first select the register with ?&FE00=17 or *FX151,0,17. The contents
of register 17 can then be read either directly from &FE01 or indirectly
with Osbyte 150, X=1. The contents of the CRTC registers 16 and 17 are
examined in the program PENTEST using Osbyte 151 (write to Sheila) and
Osbyte 150 (read from Sheila).
Connect your light pen to the analogue port and chain the program PENTEST.
Before you point a light pen at the screen notice that the light pen
register contains zero. Move the light pen around the screen and, if all
is well, you will see the contents of the light pen register changing and
hear a sound with every change. PENTEST does not use a light pen switch
and works with all light pens.
10 REM> PENTEST
20 ONERROR VDU23,1,1;0;0;0;:END
30 MODE4
40 VDU23,1,0;0;0;0;
50 VDU19,0,4;0;
60 A%=150
70 X%=1
80 REPEAT
90 *FX151,0,17
100 R%=(USR(&FFF4)AND&FF0000)DIV&10000
110 *FX151,0,16
120 S%=(USR(&FFF4)AND&FF0000)DIV&10000
130 PRINTTAB(12,14)"Low byte = &";~R%;" "
140 PRINTTAB(12,16)"High byte= &";~S%;" "
150 IF R%<>T% SOUND 1,-10,100,1
160 IF S%<>U% SOUND 1,-10,50,1
170 T%=R%
180 U%=S%
190 UNTIL FALSE
00000000 55 73 69 6e 67 20 61 20 6c 69 67 68 74 20 70 65 |Using a light pe|
00000010 6e 20 77 69 74 68 20 74 68 65 20 42 42 43 20 6d |n with the BBC m|
00000020 69 63 72 6f 63 6f 6d 70 75 74 65 72 20 2d 20 62 |icrocomputer - b|
00000030 79 20 2d 20 47 6f 72 64 6f 6e 20 48 6f 72 73 69 |y - Gordon Horsi|
00000040 6e 67 74 6f 6e 0d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |ngton.----------|
00000050 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------|
*
00000080 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 0d 0d 4d 6f 64 |-----------..Mod|
00000090 75 6c 65 20 30 2e 20 49 6e 74 72 6f 64 75 63 74 |ule 0. Introduct|
000000a0 69 6f 6e 0d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |ion.------------|
000000b0 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 0d 0d 4c 69 67 68 |----------..Ligh|
000000c0 74 20 70 65 6e 73 20 63 61 6e 20 62 65 20 75 73 |t pens can be us|
000000d0 65 64 20 77 69 74 68 20 74 68 65 20 42 42 43 20 |ed with the BBC |
000000e0 42 2c 20 42 42 43 20 42 2b 20 61 6e 64 20 4d 61 |B, BBC B+ and Ma|
000000f0 73 74 65 72 20 31 32 38 20 63 6f 6d 70 75 74 65 |ster 128 compute|
00000100 72 73 2e 0d 54 68 69 73 20 6d 6f 64 75 6c 65 20 |rs..This module |
00000110 69 6e 74 72 6f 64 75 63 65 73 20 61 20 62 6c 6f |introduces a blo|
00000120 63 6b 20 6f 66 20 73 69 78 20 6d 6f 64 75 6c 65 |ck of six module|
00000130 73 20 77 68 69 63 68 20 64 65 61 6c 20 77 69 74 |s which deal wit|
00000140 68 20 74 68 65 20 64 65 73 69 67 6e 0d 6f 66 20 |h the design.of |
00000150 62 6f 74 68 20 74 68 65 20 68 61 72 64 77 61 72 |both the hardwar|
00000160 65 20 61 6e 64 20 73 6f 66 74 77 61 72 65 20 6e |e and software n|
00000170 65 65 64 65 64 20 74 6f 20 75 73 65 20 61 20 6c |eeded to use a l|
00000180 69 67 68 74 20 70 65 6e 20 77 69 74 68 20 61 20 |ight pen with a |
00000190 42 42 43 0d 6d 69 63 72 6f 63 6f 6d 70 75 74 65 |BBC.microcompute|
000001a0 72 2e 0d 0d 54 68 65 20 73 69 78 20 6d 6f 64 75 |r...The six modu|
000001b0 6c 65 73 20 61 72 65 20 69 6e 20 66 69 6c 65 73 |les are in files|
000001c0 20 6e 61 6d 65 64 20 54 2f 50 45 4e 30 30 20 74 | named T/PEN00 t|
000001d0 6f 20 54 2f 50 45 4e 30 35 2e 20 54 68 65 20 66 |o T/PEN05. The f|
000001e0 6f 6c 6c 6f 77 69 6e 67 0d 74 6f 70 69 63 73 20 |ollowing.topics |
000001f0 77 69 6c 6c 20 62 65 20 63 6f 76 65 72 65 64 20 |will be covered |
00000200 69 6e 20 74 68 65 73 65 20 6d 6f 64 75 6c 65 73 |in these modules|
00000210 2e 0d 0d 0d 4d 6f 64 75 6c 65 20 30 2e 20 54 68 |....Module 0. Th|
00000220 69 73 20 6d 6f 64 75 6c 65 2e 20 44 65 73 69 67 |is module. Desig|
00000230 6e 69 6e 67 20 61 6e 64 20 74 65 73 74 69 6e 67 |ning and testing|
00000240 20 61 20 6c 69 67 68 74 20 70 65 6e 2e 0d 20 20 | a light pen.. |
00000250 20 20 20 20 20 20 20 20 50 72 6f 67 72 61 6d 73 | Programs|
00000260 3a 20 50 45 4e 54 45 53 54 2c 20 52 48 42 4f 4f |: PENTEST, RHBOO|
00000270 54 0d 0d 4d 6f 64 75 6c 65 20 31 2e 20 49 6e 74 |T..Module 1. Int|
00000280 72 6f 64 75 63 74 69 6f 6e 20 74 6f 20 6c 69 67 |roduction to lig|
00000290 68 74 20 70 65 6e 20 73 6f 66 74 77 61 72 65 2e |ht pen software.|
000002a0 0d 20 20 20 20 20 20 20 20 20 20 50 72 6f 67 72 |. Progr|
000002b0 61 6d 3a 20 4f 46 46 53 45 54 0d 0d 4d 6f 64 75 |am: OFFSET..Modu|
000002c0 6c 65 20 32 2e 20 4c 69 67 68 74 20 70 65 6e 20 |le 2. Light pen |
000002d0 69 6e 74 65 72 72 75 70 74 73 2e 0d 20 20 20 20 |interrupts.. |
000002e0 20 20 20 20 20 20 50 72 6f 67 72 61 6d 3a 20 49 | Program: I|
000002f0 4f 49 4e 54 45 52 0d 0d 4d 6f 64 75 6c 65 20 33 |OINTER..Module 3|
00000300 2e 20 54 75 62 65 20 63 6f 6d 70 61 74 69 62 6c |. Tube compatibl|
00000310 65 2c 20 69 6e 74 65 72 72 75 70 74 20 64 72 69 |e, interrupt dri|
00000320 76 65 6e 2c 20 73 63 72 6f 6c 6c 69 6e 67 20 6c |ven, scrolling l|
00000330 69 67 68 74 20 70 65 6e 20 73 6f 66 74 77 61 72 |ight pen softwar|
00000340 65 2e 0d 20 20 20 20 20 20 20 20 20 20 50 72 6f |e.. Pro|
00000350 67 72 61 6d 3a 20 53 50 49 4e 54 45 52 0d 0d 4d |gram: SPINTER..M|
00000360 6f 64 75 6c 65 20 34 2e 20 55 73 69 6e 67 20 61 |odule 4. Using a|
00000370 20 6c 69 67 68 74 20 70 65 6e 20 66 6f 72 20 67 | light pen for g|
00000380 72 61 70 68 69 63 73 20 69 6e 70 75 74 2e 0d 20 |raphics input.. |
00000390 20 20 20 20 20 20 20 20 20 50 72 6f 67 72 61 6d | Program|
000003a0 3a 20 47 52 41 50 48 49 43 0d 0d 4d 6f 64 75 6c |: GRAPHIC..Modul|
000003b0 65 20 35 2e 20 53 69 64 65 77 61 79 73 20 52 41 |e 5. Sideways RA|
000003c0 4d 20 6c 69 67 68 74 20 70 65 6e 20 64 72 69 76 |M light pen driv|
000003d0 65 72 73 2e 0d 20 20 20 20 20 20 20 20 20 20 50 |ers.. P|
000003e0 72 6f 67 72 61 6d 73 3a 20 53 57 54 45 58 54 2c |rograms: SWTEXT,|
000003f0 20 53 57 47 52 41 50 48 2c 20 41 52 54 49 53 54 | SWGRAPH, ARTIST|
00000400 0d 0d 0d 54 68 65 20 6c 61 74 65 72 20 6d 6f 64 |...The later mod|
00000410 75 6c 65 73 20 64 65 76 65 6c 6f 70 20 74 68 65 |ules develop the|
00000420 20 69 64 65 61 73 20 61 6e 64 20 74 65 63 68 6e | ideas and techn|
00000430 69 71 75 65 73 20 64 65 73 63 72 69 62 65 64 20 |iques described |
00000440 69 6e 20 74 68 65 0d 65 61 72 6c 69 65 72 20 6d |in the.earlier m|
00000450 6f 64 75 6c 65 73 20 61 6e 64 20 66 6f 72 20 74 |odules and for t|
00000460 68 69 73 20 72 65 61 73 6f 6e 20 74 68 65 79 20 |his reason they |
00000470 6e 65 65 64 20 74 6f 20 62 65 20 77 6f 72 6b 65 |need to be worke|
00000480 64 20 74 68 72 6f 75 67 68 20 66 72 6f 6d 0d 62 |d through from.b|
00000490 65 67 69 6e 6e 69 6e 67 20 74 6f 20 65 6e 64 20 |eginning to end |
000004a0 72 61 74 68 65 72 20 74 68 61 6e 20 75 73 65 64 |rather than used|
000004b0 20 61 73 20 61 20 72 65 66 65 72 65 6e 63 65 20 | as a reference |
000004c0 67 75 69 64 65 2e 20 49 74 20 69 73 20 65 73 73 |guide. It is ess|
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000004e0 69 74 68 65 72 20 42 41 53 49 43 20 32 20 6f 72 |ither BASIC 2 or|
000004f0 20 42 41 53 49 43 20 34 20 61 6e 64 20 6f 70 65 | BASIC 4 and ope|
00000500 72 61 74 69 6e 67 20 73 79 73 74 65 6d 20 31 2e |rating system 1.|
00000510 32 30 20 28 6f 72 20 68 69 67 68 65 72 29 0d 69 |20 (or higher).i|
00000520 6e 73 74 61 6c 6c 65 64 20 69 6e 20 79 6f 75 72 |nstalled in your|
00000530 20 63 6f 6d 70 75 74 65 72 2e 0d 0d 0d 4c 69 67 | computer....Lig|
00000540 68 74 20 70 65 6e 20 64 65 73 69 67 6e 0d 2d 2d |ht pen design.--|
00000550 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 0d 0d |--------------..|
00000560 41 20 6c 69 67 68 74 20 70 65 6e 20 67 65 6e 65 |A light pen gene|
00000570 72 61 74 65 73 20 61 20 54 54 4c 20 70 75 6c 73 |rates a TTL puls|
00000580 65 20 63 61 6c 6c 65 64 20 61 20 76 69 64 65 6f |e called a video|
00000590 20 73 74 72 6f 62 65 20 70 75 6c 73 65 20 28 56 | strobe pulse (V|
000005a0 53 50 29 20 61 6e 64 0d 74 68 65 20 74 69 6d 69 |SP) and.the timi|
000005b0 6e 67 20 6f 66 20 74 68 69 73 20 70 75 6c 73 65 |ng of this pulse|
000005c0 20 63 6f 72 72 65 73 70 6f 6e 64 73 20 77 69 74 | corresponds wit|
000005d0 68 20 74 68 65 20 70 6f 73 69 74 69 6f 6e 20 6f |h the position o|
000005e0 66 20 74 68 65 20 70 65 6e 20 6f 6e 20 74 68 65 |f the pen on the|
000005f0 0d 73 63 72 65 65 6e 2e 20 54 68 65 20 73 63 72 |.screen. The scr|
00000600 65 65 6e 20 70 6f 73 69 74 69 6f 6e 20 61 74 20 |een position at |
00000610 74 68 65 20 66 61 6c 6c 69 6e 67 20 65 64 67 65 |the falling edge|
00000620 20 6f 66 20 74 68 65 20 56 53 50 20 69 73 20 6c | of the VSP is l|
00000630 61 74 63 68 65 64 20 69 6e 74 6f 0d 74 68 65 20 |atched into.the |
00000640 31 34 20 62 69 74 20 6c 69 67 68 74 20 70 65 6e |14 bit light pen|
00000650 20 72 65 67 69 73 74 65 72 20 6f 66 20 74 68 65 | register of the|
00000660 20 36 38 34 35 20 43 52 54 43 20 69 6e 20 74 68 | 6845 CRTC in th|
00000670 65 20 63 6f 6d 70 75 74 65 72 2e 20 54 68 65 20 |e computer. The |
00000680 41 63 6f 72 6e 0d 61 70 70 72 6f 76 65 64 20 6c |Acorn.approved l|
00000690 69 67 68 74 20 70 65 6e 20 75 73 65 73 20 61 20 |ight pen uses a |
000006a0 70 75 73 68 20 74 69 70 20 6d 69 63 72 6f 20 73 |push tip micro s|
000006b0 77 69 74 63 68 20 74 6f 20 73 69 67 6e 61 6c 20 |witch to signal |
000006c0 74 6f 20 74 68 65 20 63 6f 6d 70 75 74 65 72 0d |to the computer.|
000006d0 77 68 65 6e 20 74 68 65 20 74 69 70 20 6f 66 20 |when the tip of |
000006e0 74 68 65 20 70 65 6e 20 69 73 20 74 6f 75 63 68 |the pen is touch|
000006f0 69 6e 67 20 74 68 65 20 76 69 64 65 6f 20 6d 6f |ing the video mo|
00000700 6e 69 74 6f 72 20 73 63 72 65 65 6e 2e 20 54 68 |nitor screen. Th|
00000710 65 20 73 77 69 74 63 68 0d 69 73 20 63 6f 6e 6e |e switch.is conn|
00000720 65 63 74 65 64 20 74 68 65 20 72 69 67 68 74 20 |ected the right |
00000730 66 69 72 65 20 62 75 74 74 6f 6e 20 69 6e 70 75 |fire button inpu|
00000740 74 20 28 50 42 31 20 6f 66 20 74 68 65 20 61 6e |t (PB1 of the an|
00000750 61 6c 6f 67 75 65 20 70 6f 72 74 0d 63 6f 6e 6e |alogue port.conn|
00000760 65 63 74 6f 72 29 20 61 6e 64 20 69 73 20 6e 6f |ector) and is no|
00000770 72 6d 61 6c 6c 79 20 63 6c 6f 73 65 64 2e 20 54 |rmally closed. T|
00000780 68 69 73 20 6d 65 61 6e 73 20 74 68 61 74 20 77 |his means that w|
00000790 68 65 6e 20 74 68 65 20 70 65 6e 20 69 73 0d 74 |hen the pen is.t|
000007a0 6f 75 63 68 69 6e 67 20 74 68 65 20 73 63 72 65 |ouching the scre|
000007b0 65 6e 20 74 68 65 6e 20 41 44 56 41 4c 28 30 29 |en then ADVAL(0)|
000007c0 41 4e 44 33 3d 30 2c 20 61 6e 64 20 77 68 65 6e |AND3=0, and when|
000007d0 20 74 68 65 20 70 65 6e 20 69 73 20 6e 6f 74 20 | the pen is not |
000007e0 70 72 65 73 73 65 64 0d 61 67 61 69 6e 73 74 20 |pressed.against |
000007f0 74 68 65 20 73 63 72 65 65 6e 20 41 44 56 41 4c |the screen ADVAL|
00000800 28 30 29 41 4e 44 33 3d 32 2e 20 55 73 69 6e 67 |(0)AND3=2. Using|
00000810 20 61 20 6e 6f 72 6d 61 6c 6c 79 20 63 6c 6f 73 | a normally clos|
00000820 65 64 20 73 77 69 74 63 68 20 69 73 20 71 75 69 |ed switch is qui|
00000830 74 65 0d 61 20 67 6f 6f 64 20 69 64 65 61 20 62 |te.a good idea b|
00000840 65 63 61 75 73 65 20 73 6f 66 74 77 61 72 65 20 |ecause software |
00000850 77 72 69 74 74 65 6e 20 66 6f 72 20 74 68 65 20 |written for the |
00000860 41 63 6f 72 6e 20 61 70 70 72 6f 76 65 64 20 64 |Acorn approved d|
00000870 65 73 69 67 6e 20 6c 69 67 68 74 0d 70 65 6e 20 |esign light.pen |
00000880 63 61 6e 20 62 65 20 75 73 65 64 20 77 69 74 68 |can be used with|
00000890 20 61 20 70 65 6e 20 77 68 69 63 68 20 64 6f 65 | a pen which doe|
000008a0 73 20 6e 6f 74 20 68 61 76 65 20 61 20 73 77 69 |s not have a swi|
000008b0 74 63 68 20 77 69 74 68 6f 75 74 20 6d 6f 64 69 |tch without modi|
000008c0 66 79 69 6e 67 0d 74 68 65 20 73 6f 66 74 77 61 |fying.the softwa|
000008d0 72 65 2e 20 49 66 20 79 6f 75 20 64 65 63 69 64 |re. If you decid|
000008e0 65 20 74 6f 20 6d 61 6b 65 20 79 6f 75 72 20 6f |e to make your o|
000008f0 77 6e 20 6c 69 67 68 74 20 70 65 6e 20 74 72 79 |wn light pen try|
00000900 20 74 6f 20 69 6e 63 6f 72 70 6f 72 61 74 65 0d | to incorporate.|
00000910 61 20 6e 6f 72 6d 61 6c 6c 79 20 63 6c 6f 73 65 |a normally close|
00000920 64 20 73 77 69 74 63 68 20 61 63 72 6f 73 73 20 |d switch across |
00000930 70 69 6e 20 33 20 28 30 20 56 6f 6c 74 73 29 20 |pin 3 (0 Volts) |
00000940 61 6e 64 20 70 69 6e 20 31 30 20 28 50 42 31 2c |and pin 10 (PB1,|
00000950 20 61 6c 73 6f 0d 6b 6e 6f 77 6e 20 61 73 20 49 | also.known as I|
00000960 4f 31 29 20 6f 66 20 74 68 65 20 61 6e 61 6c 6f |O1) of the analo|
00000970 67 75 65 20 70 6f 72 74 20 63 6f 6e 6e 65 63 74 |gue port connect|
00000980 6f 72 2e 0d 0d 4f 6e 6c 79 20 6f 6e 65 20 64 65 |or...Only one de|
00000990 73 69 67 6e 20 6f 66 20 6c 69 67 68 74 20 70 65 |sign of light pe|
000009a0 6e 20 68 61 73 20 62 65 65 6e 20 6f 66 66 69 63 |n has been offic|
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000009c0 79 20 41 63 6f 72 6e 20 66 6f 72 20 75 73 65 0d |y Acorn for use.|
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00002ad0 45 4e 44 0d 20 20 20 33 30 20 4d 4f 44 45 34 0d |END. 30 MODE4.|
00002ae0 20 20 20 34 30 20 56 44 55 32 33 2c 31 2c 30 3b | 40 VDU23,1,0;|
00002af0 30 3b 30 3b 30 3b 0d 20 20 20 35 30 20 56 44 55 |0;0;0;. 50 VDU|
00002b00 31 39 2c 30 2c 34 3b 30 3b 0d 20 20 20 36 30 20 |19,0,4;0;. 60 |
00002b10 41 25 3d 31 35 30 0d 20 20 20 37 30 20 58 25 3d |A%=150. 70 X%=|
00002b20 31 0d 20 20 20 38 30 20 52 45 50 45 41 54 0d 20 |1. 80 REPEAT. |
00002b30 20 20 39 30 20 2a 46 58 31 35 31 2c 30 2c 31 37 | 90 *FX151,0,17|
00002b40 0d 20 20 31 30 30 20 52 25 3d 28 55 53 52 28 26 |. 100 R%=(USR(&|
00002b50 46 46 46 34 29 41 4e 44 26 46 46 30 30 30 30 29 |FFF4)AND&FF0000)|
00002b60 44 49 56 26 31 30 30 30 30 0d 20 20 31 31 30 20 |DIV&10000. 110 |
00002b70 2a 46 58 31 35 31 2c 30 2c 31 36 0d 20 20 31 32 |*FX151,0,16. 12|
00002b80 30 20 53 25 3d 28 55 53 52 28 26 46 46 46 34 29 |0 S%=(USR(&FFF4)|
00002b90 41 4e 44 26 46 46 30 30 30 30 29 44 49 56 26 31 |AND&FF0000)DIV&1|
00002ba0 30 30 30 30 0d 20 20 31 33 30 20 50 52 49 4e 54 |0000. 130 PRINT|
00002bb0 54 41 42 28 31 32 2c 31 34 29 22 4c 6f 77 20 62 |TAB(12,14)"Low b|
00002bc0 79 74 65 20 3d 20 26 22 3b 7e 52 25 3b 22 20 22 |yte = &";~R%;" "|
00002bd0 0d 20 20 31 34 30 20 50 52 49 4e 54 54 41 42 28 |. 140 PRINTTAB(|
00002be0 31 32 2c 31 36 29 22 48 69 67 68 20 62 79 74 65 |12,16)"High byte|
00002bf0 3d 20 26 22 3b 7e 53 25 3b 22 20 22 0d 20 20 31 |= &";~S%;" ". 1|
00002c00 35 30 20 49 46 20 52 25 3c 3e 54 25 20 53 4f 55 |50 IF R%<>T% SOU|
00002c10 4e 44 20 31 2c 2d 31 30 2c 31 30 30 2c 31 0d 20 |ND 1,-10,100,1. |
00002c20 20 31 36 30 20 49 46 20 53 25 3c 3e 55 25 20 53 | 160 IF S%<>U% S|
00002c30 4f 55 4e 44 20 31 2c 2d 31 30 2c 35 30 2c 31 0d |OUND 1,-10,50,1.|
00002c40 20 20 31 37 30 20 54 25 3d 52 25 0d 20 20 31 38 | 170 T%=R%. 18|
00002c50 30 20 55 25 3d 53 25 0d 20 20 31 39 30 20 55 4e |0 U%=S%. 190 UN|
00002c60 54 49 4c 20 46 41 4c 53 45 0d |TIL FALSE.|
00002c6a 
13-01-89/T\PEN00.m0
13-01-89/T\PEN00.m1
13-01-89/T\PEN00.m2
13-01-89/T\PEN00.m4
13-01-89/T\PEN00.m5
.